Our principle objective is to assess the association between long-term exposures to air pollution and psychiatric disorders-specifically depression and anxiety-in older women. The public health burden of psychiatric disorders like depression and anxiety is tremendous. An estimated 1 in 4 individuals will experience an anxiety disorder during the lifetime making such disorders the most common psychiatric disorders in the United States. In 2000, depression ranked number one in terms of causes of Years Lived with Disability and ranked fourth among all causes of disability adjusted life years (DALYs) lost. Thus, improved understanding of the role of a modifiable risk factor for these conditions could have great health, and associated financial, benefits. Several lines of evidence suggest the likelihood of an association between air pollution and psychiatric disorders. In particular, there are well established cardiovascular effects of air pollution, and there is evidence that depression in the elderly may have a strong cardiovascular etiology. We propose a study within the Nurses' Health Study (NHS), a large prospective cohort of women (121,700 female registered nurses followed since 1976). In this cohort, we have assessed depression and anxiety using well- established, validated scales (the Mental Health Index 5-item scale [MHI-5] and the Crown-Crisp index [CCI]). In addition, we have estimates of exposures to thoracic (PM10) and fine (PM2.5) particulate air pollution, traffic-related air pollution (largely ultrafine particulates-or nanoparticles), as well as gaseous components of air pollution such as SO2, NO2, CO, and ozone (O3). Thus, we have relevant data within a very large, US-wide cohort of elderly women with which to address the novel hypothesis that long-term exposure to air pollution is related to psychiatric disorders.